Methods for producing composite elements based on foams based on isocyanate

ABSTRACT

The invention relates to a process for the production of composites, composed of at least one outer layer b) and of an isocyanate-based rigid foam a), where the outer layer b) is moved continuously and the starting material for the isocyanate-based rigid foam a) is applied to the outer layer b), which comprises achieving the application of the liquid starting material for the isocyanate-based rigid foam a) by means of at least one fixed tube c) which has openings f) and which has been placed, with respect to the outer layer b), so as to be parallel to the plane of the outer layer and at right angles to the direction of movement.

This application is a continuation of U.S. application Ser. No.12/808,570 filed Jun. 16, 2010, which is a National Stage ofPCT/EP2008/067517 filed Dec. 15, 2008, both of which are incorporatedherein by reference. This application also claims the benefit of FP07150059.9 filed Dec. 17, 2007.

The invention relates to a process for the production of compositeelements composed of at least one outer layer and of a foam-formingreaction mixture, which is applied to the lower outer layer by way of atleast one fixed tube having openings.

The production of composite elements in particular composed of metallicouter layers and of a core composed of isocyanate-based foams, mostly ofpolyurethane (PU) foams or of polyisocyanurate (PIR) foams, is widelypracticed nowadays on continuously operating twin-belt systems, theseelements often also being called sandwich elements. Elements for thedesign of façades on a very wide variety of buildings are increasinglyimportant, alongside sandwich elements for cold-store insulation. Theouter layers used here comprise not only coated steel sheet but alsostainless steel sheet, copper sheet, or aluminum sheet. Particularly inthe case of façade elements, the surface structure of the boundarybetween the foam and the outer layer is of decisive importance. Forvarious reasons, undesired air inclusions, known as vacuoles, oftenoccur between the lower outer layer and the isocyanate-based foam duringthe production of the sandwich elements. In the façade-elementapplication, these air inclusions between metal sheet and foam can causethe metal sheet to blister and make the façades unsightly, particularlyin the event of marked temperature changes and if the color shades ofthe outer layer are dark.

Adhesive between the insulating foam and the lower outer layer is alsoreduced. It is often the case that the lower outer layer in sandwichelements has the poorest adhesion, determined by the tensile test.Furthermore, the sheet metal underside is the external side of thefaçade in the usual designs produced using sandwich elements, and istherefore exposed to extreme conditions, examples being temperature andsuction effects. It is therefore subject to greater stresses than thetop side of the sandwich element, and the result of this can beseparation of the foam from the metal sheet and likewise thereforeblistering.

There is therefore a requirement to find a process which lastinglyminimizes vacuole formation at the surface of the isocyanate-based rigidfoams, or avoids this entirely, and which functions even when theproduction process is subject to adverse external circumstances. Theprocess is intended to be capable of continuous or batchwise use.Batchwise operation can, for example, be used during start-up of thetwin belt and for composite elements produced by means of pressesoperating batchwise. Continuous use takes place when twin-belt systemsare used.

In the prior-art twin-belt process, the reaction mixture is prepared bymachinery using high- or low-pressure technology, and is applied to thelower outer layer by means of oscillating rake applicators. The rakehere is stationary in the direction of running of the belt, andoscillates across the width of the element. A disadvantage of thismethod of application is that any requirement for double-overlappingonto previously applied reaction mixture applies fresh material leads toapplication of, thus giving a mixture with different reaction states.The result of this mixture is that the foam surface produced therebydoes not rise uniformly, and air is therefore included when the upperouter layer is introduced. This disadvantage becomes more marked as thetime between application of the reaction mixture and the start of thefoam reaction becomes shorter. The speed of the continuously operatingtwin belt is limited by the maximum possible oscillation speed of themixing head. Another disadvantage is that as the amount of oscillationincreases the amount of reaction mixture applied in the edge regionbecomes greater and that applied in the middle region of the outer layerbecomes smaller.

In the alternative high-speed process, the reaction mixture is appliedto the lower outer layer by way of a multi-pronged applicator, likewiseincluding air bubbles in the reaction mixture and likewise making itimpossible to produce surfaces without vacuoles. In addition, with thisapplication method the reaction mixture has to flow laterally acrossrelatively large regions, the result being production of relativelylarge vacuole zones on the lower and upper outer layer, especially inthe outermost regions, before the individual strands from themulti-pronged applicator coalesce. Furthermore, it is often possible todiscern a groove, or at least a defect in the foam, in the region wherethe strands from the multi-pronged applicator coalesce.

In order to eliminate these shortcomings, DE 197 41 523 proposes that,after application of the liquid reaction mixture for the rigid foam tothe outer layer, air is blown onto the foam mixture, which is stillflowable. The intention of this is to smooth the surface of the reactionmixture and to reduce the level of air-bubble inclusion. A firstdisadvantage here is that the blowing of air implies an additional stepin the process. The blown air can moreover produce areas of greaterthickness of the reaction mixture, and these likewise bring about anirregular surface.

It was then an object of the present invention to find an applicationprocess for a reaction mixture of an isocyanate-based rigid foam, inparticular a PU system or PIR system, to a horizontal metal sheet or toanother flexible or rigid outer layer which is continuously transportedhorizontally, this being the usual method for the production of sandwichelements by a continuously operating twin belt. The intention was thatthis lead to a surface structure improved over the prior art for thefoam on the lower outer layer, and in particular to avoidance ofvacuoles. The process was moreover intended to lead to better adhesionbetween outer layer and rigid foam. In particular, the intention wasthat the surface of the applied foam be uniform. The process wasintended to be especially suitable for rapidly initiating systems, andthe intention here was to avoid the disadvantages listed above for themultipronged applicator and for the oscillating rake applicator.

Surprisingly, the object was achieved in that the reaction mixture isapplied to the lower outer layer b) by means of at least one fixed tubec), hereinafter also termed rake applicator, which has perforations andwhich has been placed, with respect to the outer layer b), so as to beparallel and at right angles to the direction of movement.

The invention therefore provides a process for the production ofcomposites, composed of at least one outer layer b) and of anisocyanate-based rigid foam a), where the outer layer b) is movedcontinuously and the starting material for the isocyanate-based rigidfoam a) is applied to the outer layer b), which comprises achieving theapplication of the liquid starting material for the isocyanate-basedrigid foam a) by means of at least one fixed tube c) which has openingsf) and which has been placed, with respect to the outer layer b), so asto be parallel to the plane of the outer layer and at right angles tothe direction of movement.

The terms holes and perforations may be used as synonyms hereinafter.

The invention further provides an apparatus for the application ofliquid reaction mixtures to an outer layer b), where the outer layer b)is moved continuously and the starting material for the isocyanate-basedrigid foam a) is applied to the outer layer b), which comprisesachieving the application of the liquid reaction mixture to the outerlayer b) by means of at least two fixed tubes c) arranged alongside oneanother, which have openings f) and which have been placed so as to beparallel to the plane of the outer layer and at right angles to thedirection of movement of the outer layer b).

In one preferred embodiment of the invention, the arrangement of atleast two tubes c) having openings f) is in particular such that theyform a straight line. It is preferable to use from 2 to 4 tubes c),particularly preferably from 2 to 3, and in particular 2.

The inventive rake applicator has, as described, a tubular shape, withholes at the underside, distributed across the entire length, and withthe feed of the reaction mixture located either at one end of the tubesc) or preferably in their middle. If a plurality of tubes c) is used,the feed is preferably undertaken in the same manner for all of thetubes c).

The length of the tubes c), or the length of the tubes c) arrangedalongside one another, can be the same as the width of the outer layerb). It is preferable that the length of the tube c) is smaller than thewidth of the outer layer b), in order to avoid application of some ofthe reaction mixture alongside the outer layer b). The arrangement ofthe rake applicator here is in the middle above the outer layer b). Therake applicator preferably covers at least 70% of the width of the outerlayer b). If the width of the outer layer b) is 1.20 m, as is usual forsandwich elements, there would in this case be a width of 25 cm on eachside not covered by the rake applicator. It is preferable that the rakeapplicator, or the rake applicators arranged alongside one another,cover(s) at least 70% of the width of the outer layer b), particularlypreferably at least 80%, and in particular at least 95%.

The height of attachment of the rake with respect to the lower outerlayer b) is usually from 5 to 30 cm, preferably from 10 to 30 cm, and inparticular from 15 to 25 cm.

The number of the openings f) along the rake is, as a function of thelength of the rake, at least 2, preferably at least 6, particularlypreferably from 10 to 50, and in particular from 20 to 40. The number ofthe holes is preferably an even number.

The diameters of the openings f) are in the range from 0.5 to 10 mm,preferably from 1.0 mm to 4 mm. The distances between the openings f)are preferably from 5 to 200 mm, particularly preferably from 5 to 60mm, and in particular from 10 to 30 mm. This distance, and the diameter,are preferably the same over the entire length of the tube c).

The internal diameter of the tube c) is from 0.2 to 5 cm, preferablyfrom 0.3 to 2.5 cm, and in particular from 0.2 to 2 cm.

In one particularly preferred embodiment, the length of the openings f)differs over the length of the tube c). The length of the openings f)means the distance which the mixture a) has to travel from the interiorof the tube c) until it is discharged from the tube c). Various methodscan be used for this purpose. Firstly, the internal diameter of the tubec) can be altered. This is not preferred, since components of this typeare difficult to produce and to clean.

It is preferable that the length of the openings f) is altered in that ametal part is placed at the underside of the tube c) in such a way thatthe length of the perforations is altered in the desired manner. Thismeasure in fact changes the wall thickness of the tube c). The holelengths, viewed from the site of the feed of the starting material forthe isocyanate-based rigid foam a) to the end, do not decrease linearly,but decrease exponentially. The usual manner of prolongation of theopenings f) is such that the length decreases from the feed of themixture a) to the ends of the tube c). That means that if the mixture a)is fed in the middle of the tube c), the length of the openings f) fallsin the direction toward the ends. If the mixture a) is fed at the end ofthe tube c) the length of the openings f) falls in the direction fromthe side where the feed takes place to the other side.

The selection of the length of the openings f) here is preferably suchthat the ratio of the length of the openings f) from the end to themiddle for each tube c) is from 1.1 to 10. The ratio is particularlypreferably from 2.5 to 10, in particular from 5 to 10.

If a plurality of tubes c) is used, the variation of the length of theopenings f) is designed to be equal for all of the tubes c).

Each of the tubes c) having openings f) has connection to mixingequipment for the mixing of the components of the liquid startingmaterial for the isocyanate-based rigid foam a). This is usuallyachieved by means of a feed d) and e) situated therebetween. The designof this feed is that of a tube, and if a plurality of tubes c) is used,each tube has connection to the feed. This can be achieved by using atube from which in turn connection tubes run out to the tubes c). FIG. 1shows this type of apparatus using two tubes c).

The diameter of the feeds d) is preferably constant. It is preferablyfrom 4 to 30 mm, particularly preferably from 6 to 22 mm.

The inventive process is suitable for any of the isocyanate-based rigidfoams, examples being polyurethane (PU) foams and foams having urethanegroups and having isocyanurate groups, hereinafter also termed PU/PIRfoams or simply PIR foams. For many applications of the compositesproduced by the inventive process, it is preferable that a PIR foam isused as isocyanate-based rigid foam a).

The design of the inventive process is preferably such that the amountof the liquid starting material applied to the outer layer b) for theisocyanate-based rigid foam a) is from 2 kg/min to 100 kg/min,preferably from 8 kg/min to 60 kg/min.

The viscosity of the liquid starting material for the isocyanate-basedrigid foam a) is preferably from 50 mPa*s to 2000 mPa*s, particularlypreferably from 100 mPa*s to 1000 mPa*s, at 25° C.

The inventive process is particularly suitable for foams where the creamtime of the system is short. The cream time of the systems used for theinventive process is preferably below 15 s, with preference below 12 s,with particular preference below 10 s, and in particular below 8 s,while the fiber time of the system is from 20 to 60 s. Cream time is thetime between the mixing of the polyol component and the isocyanatecomponent and the start of the urethane reaction. The fiber time is thetime from the mixing of the starting components of the foams to thejuncture at which the reaction product becomes non-flowable. The fibertime is adapted appropriately as a function of the thickness of theelement produced, and also the speed of the twin belt.

In one particular embodiment of the inventive process, an adhesionpromoter can be applied between the outer layer b) and theisocyanate-based rigid foam a). The adhesion promoter used can comprisethe adhesion promoters known from the prior art. Polyurethanes are inparticular used, and it is possible here to use either reactivesingle-component systems or reactive two-component systems.

The adhesion promoter is applied in front of the tube c) havingperforations, in the direction of movement of the outer layer b). Theselection of the distance between application of the adhesion promoterand application of the starting components for the isocyanate-basedrigid foam a) here is to be such that the adhesion promoter has notentirely completed its reaction before application of the startingcomponents for the isocyanate-based rigid foam a).

The adhesion promoter can be applied to the outer layer b) by knownprocesses, such as spraying. It is preferable that the adhesion promoterhas been applied to the outer layer b) by means of a rotating flat diskwhich has been placed horizontally or with a slight deviation from thehorizontal of up to 15°, and preferably in a manner such that it isparallel to the outer layer b). The disk can be, in the simplest case,circular, or elliptical, and flat. The design of the disk is preferablyserrated or star-shaped, and the points of the star here can have anupward curve.

The disk can be completely flat, or can have upward curvature or anglingat the edge. It is preferable to use a disk whose edges have upwardcurvature or angling. Holes are introduced into the angled portion, inorder to ensure discharge of the adhesion promoter. The diameter andnumber of the holes are appropriately adjusted to one another, in orderto permit application of the adhesion promoter in finely dispersed formto the underlying outer layer b) with maximum uniformity, and to allowdischarge of all of the material applied to the disk, and to minimizethe maintenance cost of the disk.

In one embodiment, the design of the disk is of cascade type. Thearrangement of the cascades here rises from the axis of rotationoutward. At the transitions from one cascade to the adjacent cascade,there can be holes placed within the disk, so that a portion of theadhesion promoter can be discharged at these cascade transitions ontothe lower outer layer b). This type of disk designed in the manner of acascade provides particularly uniform application of the adhesionpromoter to the outer layer b) situated thereunder. The application ofthe adhesion promoter to the disk takes place at minimum distance fromthe axis of rotation. Surprisingly, it has been found here that theadhesion promoter is particularly uniformly distributed onto the lowerouter layer b) if the application point of the adhesion promoter isexactly prior to or behind the axis of rotation, in parallel with thedirection of production.

The diameter of the disk is, as a function of the width of the outerlayer b), from 0.05 to 0.3 m, preferably from 0.1 to 0.25 m,particularly preferably from 0.12 to 0.22 m, based on the long side. Itsheight of attachment above the outer layer b) to which the liquid is tohe applied is from 0.02 to 0.2 m, preferably from 0.03 to 0.18 m,particularly preferably from 0.03 to 0.15 m.

A disk having from 2 to 4 cascades, preferably from 2 to 3, particularlypreferably 2, can be used.

This type of application apparatus for the adhesion promoter isdescribed by way of example in WO 2006/029786.

The inventive process and the apparatus described are particularlysuitable for systems using physical blowing agents, in particularpentanes. The inventive process is moreover preferred for the productionof composite elements with rigid outer layers.

The outer layer b) used can comprise flexible or rigid, preferablyrigid, outer layers, examples being gypsum plasterboard, glass tile,aluminum foils, aluminum sheet, copper sheet, or steel sheet, preferablyaluminum foils, or aluminum sheet or steel sheet, particularlypreferably steel sheet. The steel sheet can be coated or uncoated sheet.The steel sheet can be pretreated, for example using corona treatment,arc treatment, plasma treatment, or other conventional methods.

The outer layer b) is preferably transported at a constant speed of from1 to 60 m/min, preferably from 2 to 150 m/min, particularly preferablyfrom 2.5 to 30 m/min, and in particular from 2.5 to 20 m/min. The outerlayer b) here is in a horizontal position at least from the applicationof the foam system b) onward, and preferably during the entire periodfrom the application of the adhesion promoter.

In the inventive process, when using sheet and foils as outer layers,the outer layers are unwound in succession from a roll, if appropriateprofiled, and heated, and if appropriate pretreated, in order toincrease ease of application of polyurethane foam, and the adhesionpromoter is optionally applied, the starting material for theisocyanate-based rigid foam a) is applied by means of the inventivestationary rake, and hardened in the twin-belt system, and the productis finally cut to the desired length.

The isocyanate-based rigid foams a) used for the inventive process areproduced in a conventional and known manner, via reaction ofpolyisocyanates with compounds having at least two hydrogen atomsreactive with isocyanate groups, in the presence of blowing agents,catalysts, and conventional auxiliaries and/or additives. Details of thestarting materials used are as follows.

Organic polyisocyanates that can be used are any of the known organicdi- and polyisocyanates, preferably aromatic polyfunctional isocyanates.

Individual examples which may be mentioned are tolylene 2,4- and2,6-diisocyanate (TDI) and the corresponding isomer mixtures,diphenylmethane 4,4′-, 2,4′- and 2,2′-diisocyanate (MDI) and thecorresponding isomer mixtures, mixtures composed of diphenylmethane4,4′- and 2,4′-diisocyanates, polyphenyl polymethylene polyisocyanates,mixtures composed of diphenylmethane 4,4′-, 2,4′- and 2,2′-diisocyanatesand of polyphenyl polymethylene polyisocyanates (crude MDI) and mixturescomposed of crude MDI and of tolylene diisocyanates. The organic di- andpolyisocyanates may be used individually or in the form of mixtures.

Use is also often made of what are known as modified polyfunctionalisocyanates, i.e. products obtained via chemical reaction of organic di-and/or polyisocyanates. By way of example, mention may be made of di-and/or polyisocyanates containing uretdione groups, carbamate groups,isocyanurate groups, carbodiimide groups, allophanate groups and/orurethane groups. The modified polyisocyanates may, if appropriate, bemixed with one another or with unmodified organic polyisocyanates, suchas diphenylmethane 2,4′- or 4,4′-diisocyanate, crude MDI, or tolylene2,4- and/or 2,6-diisocyanate.

Use may also be made here of reaction products of polyfunctionalisocyanates with polyhydric polyols, or else of mixtures of these withother di- and polyisocyanates.

An organic polyisocyanate which has proven particularly successful iscrude MDI, in particular with NCO content of from 29 to 33% by weightand a viscosity at 25° C. in the range from 150 to 1000 mPas.

Compounds which may be used and which have at least two hydrogen atomsreactive toward isocyanate groups are those which bear at least tworeactive groups selected from OH groups, SH groups, NH groups, NH₂groups, and acidic CH groups, preferably OH groups, and in particularpolyether alcohols and/or polyester alcohols whose OH numbers are in therange from 25 to 800 mg KOH/g.

The polyester alcohols used are mostly prepared via condensation ofpolyhydric alcohols, preferably diols, having from 2 to 12 carbon atoms,preferably from 2 to 6 carbon atoms, with polybasic carboxylic acidshaving from 2 to 12 carbon atoms, e.g. succinic acid, glutaric acid,adipic acid, suberic acid, azelaic acid, sebacic acid,decanedicarboxylic acid, maleic acid, fumaric acid, or preferablyphthalic acid, isophthalic acid, terephthalic acid, or the isomericnaphthalenedicarboxylic acids.

The polyesterols used mostly have a functionality of from 1.5 to 4.

Polyether polyols particularly used are those prepared by knownprocesses, e.g. via anionic ppolymerization of alkylene oxides ontoH-functional starter substances in the presence of catalysts, preferablyalkali metal hydroxides or double-metal-cyanide catalysts (DMCcatalysts).

Alkylene oxides used are mostly ethylene oxide or propylene oxide, orelse tetrahydrofuran, various butylene oxides, or styrene oxide, andpreferably pure propylene 1,2-oxide. The alkylene oxides can be usedalone, in alternating succession, or in the form of a mixture.

Starter substances particularly used are compounds having at least 2,preferably from 2 to 8, hydroxy groups or having at least two primaryamino groups in the molecule.

Starter substances used and having at least 2, preferably from 2 to 8,hydroxy groups in the molecule are preferably trimethylolpropane,glycerol, pentaerythritol, sugar compounds, such as glucose, sorbitol,mannitol, and sucrose, polyhydric phenols, resols, e.g. oligomericcondensates composed of phenol and formaldehyde, and Mannich condensatescomposed of phenols, of formaldehyde, and of dialkanolarnines, and alsomelamine.

Starter substances used and having at least two primary amino groups inthe molecule are preferably aromatic di- and/or polyamines, such asphenylenediamines, 2,3-, 2,4-, 3,4-, and 2,6-tolylenediamine, and 4,4′-,2,4′-, and 2,2′-diaminodiphenylmethane, and also aliphatic di- andpolyamines, such as ethylenediamine.

The preferred functionality of the polyether polyols is from 2 to 8 andtheir preferred hydroxy numbers are from 25 to 800 mg KOH/g, inparticular from 150 to 570 mg KOH/g.

Other compounds having at least two hydrogen atoms reactive towardisocyanate are crosslinking agents and chain extenders which may be usedconcomitantly, if appropriate. Addition of difunctional chain extenders,trifunctional or higher-functionality crosslinking agents, or else, ifappropriate, mixtures of these can prove advantageous for modificationof mechanical properties. Chain extenders and/or crosslinking agentspreferably used are alkanolamines and in particular diols and/or triolswith molecular weights below 400, preferably from 60 to 300.

The amount advantageously used of chain extenders, crosslinking agents,or mixtures of these is from 1 to 20% by weight, preferably from 2 to 5%by weight, based on the polyol component.

The rigid foams are usually produced in the presence of blowing agents,catalysts, flame retardants, and cell stabilizers, and, if necessary, ofother auxiliaries and/or additives.

Blowing agents which can be used are chemical blowing agents, such aswater and/or formic acid, these reacting with isocyanate groups withelimination of carbon dioxide and, respectively, carbon dioxide andcarbon monoxide. The compounds known as physical blowing agents canpreferably also be used in combination with water or preferably insteadof water. These are compounds inert with respect to the startingcomponents, mostly liquid at room temperature, and evaporating under theconditions of the urethane reaction. The boiling point of thesecompounds is preferably below 50° C. Among the physical blowing agentsare also compounds which are gaseous at room temperature and which areintroduced or dissolved into the starting components under pressure,examples being carbon dioxide, low-boiling alkanes, and fluoroalkanes.

The blowing agents are mostly selected from the group consisting ofalkanes, formic acid and and/or cycloalkanes having at least 4 carbonatoms, dialkyl ethers, esters, ketones, acetals, fluoroalkanes havingfrom 1 to 8 carbon atoms, and tetraalkylsilanes having from 1 to 3carbon atoms in the alkyl chain, in particular tetramethylsilane.

Examples which may be mentioned are propane, n-butane, isobutane,cyclobutane, n-pentane, isopentane, cyclopentane, cyclohexane, dimethylether, methyl ethyl ether, methyl butyl ether, methyl formate, acetone,and also fluoroalkanes which can be degraded in the troposphere andtherefore do not damage the ozone layer, e.g. trifluoromethane,difluoromethane, 1,1,1,3,3-pentafluorobutane,1,1,1,3,3-pentafluoro-propane, 1,1,1,2-tetrafluoroethane,difluoroethane, and heptafluoropropane. The physical blowing agentsmentioned may be used alone or in any desired combinations with oneanother.

A mixture composed of formic acid, water, and pentane is particularlypreferred as blowing agent mixture.

The usual amount used of the blowing agent component is from 1 to 45% byweight, preferably from 1 to 30% by weight, particularly preferably from1.5 to 20% by weight, and in particular from 2 to 15% by weight, basedon the total weight of the following components: polyol, blowing agent,catalyst system, and any foam stabilizers, flame retardants, and otheradditives.

The polyurethane foams or polyisocyanurate foams usually comprise flameretardants. It is preferable to use bromine-free flame retardants. Flameretardants comprising phosphorus atoms are particularly preferred, anduse is particularly made of trischloroisopropyl phosphate, diethylethanephosphonate, triethyl phosphate, and/or diphenyl cresyl phosphate.

Catalysts used in particular comprise compounds which markedlyaccelerate the reaction of the isocyanate groups with the groupsreactive with isocyanate groups. Examples of these catalysts are basicamines, e.g. secondary aliphatic amines, imidazoles, amidines, and alsoalkanolamines, Lewis acids, or organometallic compounds, in particularthose based on tin. Catalyst systems composed of a mixture of variouscatalysts can also be used.

If isocyanurate groups are to be incorporated in the rigid foam,specific catalysts are needed. Isocyanurate catalysts usually used aremetal carboxylates, in particular potassium acetate and its solutions.The catalysts may be used alone or in any desired mixture with oneanother, as required.

Auxiliaries and/or additives which may be used are substances known perse for this purpose, e.g. surfactants, foam stabilizers, cellregulators, fillers, pigments, dyes, antioxidants, hydrolysisstabilizers, antistatic agents, fungistatic agents, and bacteriostaticagents.

Further details concerning the starting materials used for carrying outthe inventive process, blowing agents, catalysts, and also auxiliariesand/or additives are found by way of example in Kunststoffhandbuch[Plastics Handbook], volume 7, “Polyurethane” [“Polyurethanes”]Carl-Hanser-Verlag Munich, 1st edition, 1966, 2nd edition, 1983, and 3rdedition, 1993.

To produce the rigid isocyanate-based foams a) the polyisocyanates andthe compounds having at least two hydrogen atoms reactive towardisocyanate groups are reacted in amounts such that the isocyanate indexfor the polyurethane foams is in the range from 100 to 220, preferablyfrom 115 to 180.

The index that can be used for operations in the production ofpolyisocyanurate foams can also be >180, generally from 180 to 700,preferably from 200 to 550, particularly preferably from 250 to 500, andin particular from 270 to 400.

The rigid polyurethane foams can be produced batchwise or continuouslywith the aid of known mixing apparatuses. Known mixing apparatuses canbe used to mix the starting components.

The inventive rigid isocyanate-based foams a) are usually produced bythe two-component process. In this process, the compounds having atleast two hydrogen atoms reactive toward isocyanate groups are mixedwith the blowing agents, with the catalysts, and also with the otherauxiliaries and/or additives to give what is known as a polyolcomponent, and this is reacted with the polyisocyanates or mixturescomposed of the polyisocyanates and, if appropriate, blowing agents,also termed the isocyanate component.

The starting components are usually mixed at a temperature of from 15 to35° C., preferably from 20 to 30° C. The reaction mixture may be mixedusing high- or low-pressure feed machinery.

The density of the rigid foams produced is preferably from 10 to 400kg/m³, preferably from 20 to 200 kg/m³, in particular from 30 to 100kg/m³.

The thickness of the composite elements is usually in the range from 5to 250 mm.

FIG. 1 shows the inventive apparatus using two tubes c).

A more detailed description of the invention will be given in theexamples below.

EXAMPLES

A) Constitution of a PU System

Polyol Component (A Component)

44 parts of polyetherol 1 composed of propylene oxide and of an aminicstarter, functionality 4, hydroxy number 400 mg KOH/g 26 parts ofpolyetherol 2 composed of propylene oxide and saccharose as starter, OHnumber 400 mg KOH/g  5 parts of polyetherol 3 composed of propyleneoxide and trimethylolpropane as starter, OH number 200 mg KOH/g 20 partsof flame retardant 1: trischloroisopropyl phosphate, TCPP  2 parts ofsilicone-containing stabilizer  2 parts of catalyst 1: amine-containingPU catalyst  1 part of catalyst 2: amine-containing blowing catalystBlowing agent 1: n-pentane Blowing agent 2: water Blowing agent 3: 85%strength aqueous formic acid

Isocyanate Component (B Component)

Lupranat M50 isocyanate: polymeric MDI (BASF AG), NCO content: 31%,viscosity: 500 mPas at 25° C.

A component, B component, and blowing agent were reacted in ratios suchthat the index was in the region of 130 and the envelope densityachieved was 39 g/l.

B) Constitution of a PIR System

Polyol Component (A Component)

 66 parts of polyesterol 1 composed of phthalic anhydride, diethyleneglycol, and oleic acid, functionality: 1.8, hydroxy number: 200 mg KOH/g 30 parts of flame retardant 1: trischloroisopropyl phosphate, TCPP 1.5parts of stabilizer 1, silicone-containing stabilizer 1.5 parts ofcatalyst 1, PIR catalyst, salt of a carboxylic acid   1 part of catalyst2, amine-containing PU catalyst Blowing agent 1: n-pentane Blowing agent2: water Blowing agent 3: 85% strength aqueous formic acid

Isocyanate Component (B Component)

Lupranat M50 isocyanate: polymeric MDI (BASF AG), NCO content: 31%,viscosity: 500 mPas at 25° C.

The polyol component and the isocyanate component, and also the blowingagent, were mixed with one another in ratios such that the index was inthe region of 350 and the envelope density achieved was 43 g/l.

The polyurethane system and, respectively, polyisocyanurate system a)was applied in succession by means of an oscillating rake applicator andof a stationary rake applicator, composed of two equal-length tubes c)arranged in a row.

The dimensions of the oscillating rake applicator were 25 cm×1.5 cm, andit had 41 holes with diameter 1.6 mm and with a distance of 5 mm betweenthe holes, and it oscillated with a speed of 0.7 m/s across a distanceof 1.0 m.

The dimensions of the stationary rake were 95 cm×15 cm, and it had 24holes with diameter 2.8 mm and with a distance of 40 mm between theholes. The lengths of the holes of the openings f) for each of the twotubes c) rose exponentially from the end to the middle, beginning from 3mm, as far as 19 mm.

The application rate for both rake systems was 25.1 kg/min.

The metallic outer layer was not corona-treated. The width of the twinbelt was 1.2 m and it was advanced at a constant speed of 5.0 m/min. Thetemperature of the metal sheet was 37° C., and that of the twin belt wasset to 40° C. (PU) and, respectively, 60° C. (PIR). The thickness of thesandwich element was 100 mm

After hardening of the system, test specimens of dimensions 100×100×5 mmwere removed by sawing, and the adhesion of the foam to the outer layerwas determined to DIN EN ISO 527-1/DIN 53292.

The frequency of surface defects was determined quantitatively by anoptical method. For this, a plane was introduced into a foam specimen ata distance of one millimeter from the lower outer layer, i.e. from theouter layer on which the polyurethane reaction solution has been appliedin the twin-belt process, and material above the plane was removed. Theresultant foam surface was illuminated with an aperture angle of 5°, andthe area covered by shadow due to surface defect was calculated as aratio of the total surface area. For this, the illuminated foam surfacewas photographed, and the foam images were then digitized. Theintegrated area of the black regions of the digitized images wascalculated as a ratio to the total area of the images, thus providing ameasure of the frequency of surface defects. An additional qualitativeassessment of surface quality was made on the foams, the outer layerbeing removed from a foam specimen measuring 1 m×2 m and the surfacebeing assessed visually.

The various tests using different rigid foam systems with oscillatingand stationary rake applicator are compared in table 1.

TABLE 1 Experimental parameters and results. Uniformity of applicationacross the surface of the outer layer is assessed here. CompressiveTensile Compressive modulus of Tensile modulus of Number of Example FoamRake strength elasticity strength elasticity vacuoles/surface No. systemsystem [N/mm²] [N/mm²] [N/mm²] [N/mm²] Pattern defects 1 (C) PU oscill.0.14 2.7 0.10 4.1 Grooved 10% pattern 2 PU stationary 0.18 3.4 0.14 4.5Flat, no 2% pattern 3 (C) PIR oscill. 0.13 3.1 0.10 3.9 Grooved 12%pattern 4 PIR stationary 0.18 4.2 0.17 5.5 Flat, no 1% pattern C =comparative example

The results in table 1 show that the frequency of formation of surfacedefects at the boundary with the metallic outer layers is markedlyreduced, in comparison with the prior art, through use of the inventivestationary rake applicator, and that the mechanical properties of thefoam are improved, as also is the adhesion between rigid foam and outerlayer.

1. A process for the production of composites, comprising at least oneouter layer and of an isocyanate-based rigid foam, where the outer layeris moved continuously and a liquid starting material for theisocyanate-based rigid foam is applied to the outer layer, whichcomprises achieving an application of the liquid starting material forthe isocyanate-based rigid foam through at least two fixed tubes, eachof which has openings and which have been placed, with respect to theouter layer, so as to be parallel to the plane of the outer layer and atright angles to the direction of movement.
 2. The process according toclaim 1, wherein the tubes whose length direction are each at rightangles to the direction of movement are arranged alongside one another.3. The process according to claim 2, wherein the arrangement of thetubes is such that their lengths form a straight line.
 4. The processaccording to claim 1, wherein the tubes extend over at least 70% of thewidth of the outer layer, and at each of the edges of the outer layerthere is a region of equal width not covered by the tubes.
 5. Theprocess according to claim 1, wherein the tubes extend over at least 80%of the width of the outer layer, and at each of the edges of the outerlayer there is a region of equal width not covered by the tubes.
 6. Theprocess according to claim 1, wherein the tubes have been placed at aheight of from 5 to 30 cm above the outer layer.
 7. The processaccording to claim 1, wherein the diameter of the tubes is from 0.2 to 5cm.
 8. The process according to claim 1, wherein the internal diameterof the tubes remains constant from the middle to the ends of each tube.9. The process according to claim 1, wherein the length of the openingsdecreases from the middle to the ends of each tube.
 10. The processaccording to claim 1, wherein the variation of the length of theopenings of each tube is the same in all of the tubes.
 11. The processaccording to claim 1, wherein the ratio of the lengths of the openingsbetween the site of the feed of the starting material for theisocyanate-based rigid foam and the end of each tube is from 1.1 to 20.12. The process according to claim 1, wherein the liquid startingmaterial for the isocyanate-based rigid foam is fed from one end of eachtube, and the length of the openings decreases from that end to theother end of each tube.
 13. The process according to claim 1, whereinthe liquid starting material for the isocyanate-based rigid foam is fedfrom the middle of each tube, and the length of the openings decreasesfrom the middle to the ends of each tube.
 14. The process according toclaim 1, wherein the liquid starting material for the isocyanate-basedrigid foam is fed from one end of each tube.
 15. The process accordingto claim 1, wherein the diameter of the openings from 0.5 to 10 mm. 16.The process according to claim 1, wherein the distance between theopenings is from 5 to 200 mm
 17. The process according to claim 1,wherein the diameter of the openings is the same over the entire lengthof each tube.
 18. The process according to claim 1, wherein the distancebetween the openings is the same over the entire length of each tube.19. The process according to claim 1, wherein the number of the openingsof each tube is even.
 20. The process according to claim 1, wherein thenumber of the openings of each tube is ≧6.
 21. The process according toclaim 1, wherein mixing of the components of the liquid startingmaterial for the isocyanate-based rigid foam takes place in mixingequipment which has connection by way of feeds to all of the tubes. 22.The process according to claim 1, wherein each of the tubes hasconnection to precisely one feed.
 23. The process according to claim 1,wherein each of the tubes has connection to mixing equipment for themixing of the components of the liquid starting material for theisocyanate-based rigid foam.
 24. The process according to claim 21,wherein the diameter of the feeds is constant.
 25. The process accordingto claim 21, wherein the diameter of the feeds is from 4 to 30 mm. 26.The process according to claim 1, wherein the isocyanate-based rigidfoam comprises isocyanurate groups.
 27. The process according to claim1, wherein the viscosity of the liquid starting material for theisocyanate-based rigid foam is from 50 mPa*s to 2000 mPa*s at 25° C. 28.The process according to claim 1, wherein the amount of the liquidstarting material applied to the outer layer for the isocyanate-basedrigid foam is from 2 kg/min to 100 kg/min.
 29. A process for theproduction of composites, comprising at least one outer layer and of anisocyanate-based rigid foam, where the outer layer is moved continuouslyand a liquid starting material for the isocyanate-based rigid foam isapplied to the outer layer, which comprises achieving an application ofthe liquid starting material for the isocyanate-based rigid foam throughat least two fixed tubes, each of which has openings and which has beenplaced, with respect to the outer layer, so as to be parallel to theplane of the outer layer.
 30. An apparatus for the application ofliquids to a layer comprising: at least two fixed tubes arrangedalongside one another and each at right angles to the direction ofmovement of a layer moving continuously, and which tubes have openingsfor application of a liquid to the layer, and which tubes have beenplaced so as to be parallel to the plane of the layer.